* {
    margin: 0;
    padding: 0;
}

html {
    font-size: 10px;
    background: url('../images/background.png');
    background-size: cover;
}

.box {
    display: flex;
    flex: 1;
    min-height: 100vh;
    align-items: center;
    justify-content: center;
}

.key {
    width: 10rem;
    font-size: 1.5rem;
    margin: 1rem;
    padding: 1rem .5rem;
    text-align: center;
    color: #fff;
    background: rgba(0, 0, 0, .4);
    border: .4rem solid black;
    border-radius: .5rem;
    text-shadow: 0 0 .5rem black;
    transition: all .6s ease;
}

kbd {
    display: block;
    font-size: 4rem;
}

.sound {
    font-size: 1.2rem;
    color: #ff3040;
    letter-spacing: 0.1rem;
    /* 文字大写 */
    text-transform: uppercase;
}

.playing {
    transform: scale(1.1);
    border-color: #ff3040;
    box-shadow: 0 0 1rem #ff3040;
}